1. Field of the Invention
The present disclosure relates to sensors, and more particularly to flame sensors such as used in flame and smoke detectors.
2. Description of Related Art
Flame detectors can be used to detect flames as small as those produced by a lit match stick. This is useful, for example, to sound an alarm if a fire breaks out indoors. Ultraviolet (UV) sensors can be particularly useful in detecting the radiation from flames in this type of application. However, since there are non-flame sources of UV radiation, including sunlight, careful design is required to avoid false alarms. One solution to this problem is to use a UV sensor sensitive to UV-C radiation, and non-sensitive to UV-B radiation, since UV-C radiation from the sun is filtered out by the atmosphere, whereas the atmosphere allows a portion of solar UV-B radiation to reach the surface. Such sensors will not give rise to a false alarm when receiving solar radiation, such as in a room with an exterior window. UV phototubes can provide the sharp cutoff between UV-C and UV-B radiation necessary for this purpose. However, when compared to sensors typically used in residential settings, for example, UV phototubes are relatively costly, as are filters for general UV sensors that filter out UV-B radiation. UV phototubes also require relatively high voltages and are relatively fragile.
Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for improved flame detectors. The present disclosure provides a solution for this need.